1. Field of the Invention
The present invention relates to an extension rod assembly for a screw driving device, and more particularly to an extension rod assembly that has a wider application and can enable the tool head to be replaced more easily.
2. Description of the Prior Arts
An automatic screw driving tool is generally provided with an extension rod assembly, an end of the extension rod assembly is connected with a replaceable tool head, while another end of the extension rod assembly is clamped and rotated by the screw driving tool. The tool head connected to the extension rod assembly, in turn, will be rotated to tighten or loosen a screw. In operation, the extension rod can produce a magnetic force to pick up the screw automatically.
As shown in FIGS. 1 and 2, TW Patent 94103623 discloses an extension rod assembly comprises: a base 11, a slide sleeve 12, a spring 13, a fixing ring 14 and a magnetic iron 15. The base 11 is provided for insertion of a rod 111 and a tool head 112. The slide sleeve 12 is moveably mounted on the rod 11. The spring 13 is mounted on the rod 11 and biased between the shoulder 113 of the rod 11 and the slide sleeve 12. The fixing ring 14 is mounted on the rod 11. The magnetic iron 15 is disposed at an end of the slide sleeve 12 for passage of the tool head 112, so that the tool head 112 can pick up screw automatically.
In operation, however, this extension rod assembly still has the following disadvantages that need to be improved:
First, as can be seen in FIG. 2, the slide sleeve 12 is only able to move towards the tool head 112 but unable to move in the opposite direction (toward the rod 111), so if the tool head 112 only projects slightly out of the slide sleeve 12, then it will be a problem to pull the tool head 112 out of the slide sleeve 12 and replace it.
Second, although the replacement can be done by clamping the head of the tool head 112 with a clamping device, the clamping activity may cause damage to the tool head 112.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.